Ana R. F. CARREIRA1, António COELHO1, Filipe H. B. SOSA1, Nicolas SCHAEFFER1, Helena PASSOS1, João A. P. COUTINHO1
1University of Aveiro, Aveiro, Portugal
Metal scarcity is fueling the transition from ore to “urban” mining by using secondary metal sources, such as catalytic converters (CC). CCs are rich in critical metals, including platinum group (PGMs) and rare earth metals. This work presents an alternative approach for the recovery of PGMs from used automobile CC wastes. The used automobile CC was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Aiming to develop a greener process, concentrated salt solutions of AlCl3·6H2O and Al(NO3)3·9H2O were used as leaching agents for PGMs as an inorganic substitute for aqua regia. A first leaching step was performed to selectively extract rare earth metals, followed by leaching with an aluminum salt brine. The influence of the AlCl3·6H2O and Al(NO3)3·9H2O ratio, temperature, solid:liquid ratio, temperature and kinetics was evaluated. To fully valorize the recovered metals, liquid-liquid extraction systems based on ionic liquids were used to selectively separate the PGMs by anion exchange. The proposed process is an efficient and sustainable alternative for the selective recovery of metals from used CC.